Recently, a MIMO system has attracted attention as a wideband wireless mobile communication technology. The MIMO system serves to raise spectrum efficiency in proportion to the number of antennas, which is difficult to achieve in a communication technique employing a conventional single-input single-output (SISO) scheme. MIMO technology refers to a multiple antenna technique for implementing high-speed communication using a plurality of antennas. The MIMO technology is classified into a spatial multiplexing scheme and a spatial diversity scheme, according to whether the same data is transmitted or different data is transmitted.
In the spatial multiplexing scheme, different data is simultaneously transmitted through multiple transmit (Tx) antennas, such that data can be transmitted at high speed without increasing a system bandwidth. Namely, a transmitting side transmits different data using transmit (Tx) antennas and a receiving side discriminates the transmitted data through interference elimination and signal processing, thereby improving transmission rate in proportion to the number of transmit antennas.
The spatial diversity scheme serves to obtain transmit (Tx) diversity by transmitting the same data using multiple transmit (Tx) antennas. The spatial diversity scheme is a kind of a space-time channel coding scheme. The spatial diversity scheme can maximally obtain a transmit diversity gain (performance gain) by transmitting the same data through multiple transmit antennas. The spatial diversity scheme, however, is not a method for improving the transmission rate but a method for improving the reliability of transmission by the diversity gain.
The MIMO technology may be divided into an open-loop type (e.g., Bell labs layered space-time (BLAST), space-time trellis code (STTC), etc.) and a closed-loop type (e.g., transmit adaptive array (TxAA), etc.) according to whether channel information is fed back from a receiving side to a transmitting side. The open loop scheme includes a Bell Laboratories Layered Space-Time (BLAST) in which a transmission side transmits information in parallel, and a reception side detects a signal using a Zero Forcing (ZF) scheme and a Minimum Mean Square Error (MMSE) scheme repeatedly so as to increase the amount of information in proportion to the number of Tx antennas, and also includes a Space-Time Trellis Code (STTC) scheme for obtaining transmission diversity and coding gain using a space domain. The closed loop scheme includes a Transmit Antenna Array (TxAA) scheme, or the like.
FIG. 1 is a conceptual diagram of a Coordinated Multi-Point (CoMP) of the existing intra eNBs and inter eNBs.
Referring to FIG. 1, intra eNBs 110 and 120 and an inter eNB 130 exist in a multi-cell environment. In a Long Term Evolution (LTE) system, an intra eNB covers a plurality of cells (or sectors). Cells covered by an eNB to which a User Equipment (UE) belongs are in an intra eNB relationship with the UE. That is, cells covered by the same eNB that manages a cell in which a UE is located are cells corresponding to the intra eNBs 110 and 120, and cells covered by a different eNB from the eNB that manages the serving cell of the UE are cells corresponding to the inter eNB 130.
Cells covered by the same eNB that serves a UE exchange information (e.g. data and Channel State Information (CSI)) through an x2 interface, while cells covered by a different eNB from the serving eNB of the UE exchange inter-cell information via a backhaul 140. As illustrated in FIG. 1, a single-cell MIMO user 150 located in a single cell (or sector) may communicate with one serving eNB in the cell (or sector), and a multi-cell MIMO user 160 located at a cell edge may communicate with a plurality of serving eNBs in a plurality of cells (or sectors).
The CoMP scheme has been proposed to improve the throughput of a user at a cell edge by applying advanced MIMO in a multi-cell environment. Application of the CoMP scheme to a wireless communication system may not only reduce Inter-Cell Interference (ICI) in the multi-cell environment but may also allow a UE to receive joint data support from multi-cell eNBs. Also, each eNB may improve system performance by simultaneously supporting one or more UEs (or Mobile Stations (MSs)) MS1, MS2, . . . , MSK using the same radio frequency resources. Further, an eNB may implement Space Division Multiple Access (SDMA) based on CSIs between the eNB and UEs.
The CoMP operation mode may be classified into two modes, a joint processing mode which is cooperative MIMO based on data sharing and a Coordinated Scheduling/Beamforming (CS/CB) mode.
In a CoMP wireless communication system, a serving eNB and one or more neighbor eNBs (or Base Stations (BSs)) BS1, BS2, . . . , BSM are connected to a scheduler over a backbone network. The scheduler receives feedback channel information representing channel states between the UEs MS1 to MSK and the neighbor eNBs BS1, BS2, . . . , BSM, as measured by the eNBs. For example, the scheduler may schedule cooperative MIMO information for the serving eNB and the one or more cooperating eNBs. That is, the scheduler issues a command related to a cooperative MIMO operation directly to each eNB.
The CoMP system involves a geographically spaced transmission process (e.g. multi-antenna) as well as joint processing and coordinated scheduling/beamforming techniques between cells. The communication performance of a UE at a cell edge can be improved by CoMP in the multi-cell environment.
However, the existing LTE system does not include an eNB ID for allowing a UE to discriminate between an intra eNB and an inter eNB. Therefore, additional information for enabling the UE to discriminate between the intra eNB and the inter eNB is needed. In addition, although the UE discriminates between the intra eNB and the inter eNB, it is impossible for the UE to recognize which CoMP is to be applied to each intra eNB or each inter eNB. In this case, it is impossible for the UE to properly operate in response to a current situation, such that it is difficult to improve a communication performance of a cell-edge UE.